Field of the Disclosure
Embodiments of this disclosure relate to a backlight unit for a liquid crystal display device.
Discussion of the Related Art
Liquid crystal displays have been widely used in various application fields because of advantages such as miniaturization, thin profile, and low power consumption. The liquid crystal displays have been used in notebook personal computers, office automatic equipments, audio/video equipments, indoor or outdoor signboards and so on. Transmissive liquid crystal displays control electric field applied to a liquid crystal layer and modulate light from a backlight unit to display images on a screen.
The backlight unit is classified into a direct type backlight unit and an edge type backlight unit. The direct type backlight unit has a structure that a plurality of light sources are arranged below a light guide plate to allow light to directly proceed to a front surface of an liquid crystal panel. The edge type backlight unit has a structure that a plurality of light sources are disposed to face a side of a light guide plate and a plurality of optical sheets are disposed between a liquid crystal panel and the light guide plate. In the edge type backlight unit, when the light sources irradiate light to one side of the light guide plate, the light guide plate converts linear light or point light emitted from the light sources into planar light and makes the planar light proceed to a front surface the liquid crystal panel.
The backlight unit includes a guide structure which guides the light guide plate or the diffusion plate according to expansion, shrink or displacement of the light guide plate or the diffusion plate caused by temperature variation, humidity variation, vibration or shock. The guide structure of the light guide plate or the diffusion plate is implemented by a protrusion structure having a pin shape which is inserted into a groove formed in edge of the light guide plate or the diffusion plate. In general, the guide structure is protruded from a cover bottom which constitutes a lower sash. The protrusion structure is known as a cauking pin or a guide pin, and is disclosed in Korean Patent Application Publication Nos. 10-2011-0059955 (Jun. 8, 2011) and 10-2005-0121047 (Dec. 26, 2005).
The cost of manufacturing the cover bottom rises because the cauking pin is made of the same metal material as the cover bottom in general and is integral with the cover bottom. That is, the cauking pin makes the manufacturing cost of the cover bottom high. If a thickness of the cover bottom is formed thin in order to resolve the problem of the cost, the cauking pin is easily bended. The cover bottom has to have a sufficient number of the cauking pins so as to stably guide the light guide plate or the diffusion plate because the cauking pin is point-contacted with the light guide plate or the diffusion plate. However, the cauking pin made from metal material reflects light. Accordingly, there is a problem that light by reflected by the cauking pins is displayed on a screen of the liquid crystal display panel to degrade image quality.